1 Field of the Invention
This invention relates to mobile surface treating apparatus in which abrasive is impacted against the surface to be treated, removed from the surface to prevent substantial accumulation of spent abrasive on the surface, and recycled for subsequent use in the apparatus.
2. Description of the Prior Art
The cleaning of large surfaces, e.g., metal, concrete and the like, may be periodically desired, for instance, to prepare the surface for painting. In the past, air blasting with crushed slag or sand has been employed to clean the surface; however, air blasting requires compressed air which is often expensive and often contains moisture such that, for instance, the reoxidation of a treated metal surface prior to the application of protective coatings may be increased. Additionally, air blasting generally requires a larger labor force. Moreover, the abrasives commonly employed in air blasing, such as crushed slag, are subject to considerable disintegration on impact with the surface being treated, and thus are generally not recycled. Further labor is required to effect clean-up of spent abrasive in the area of the surface treating operation. Also, air blasing can be an environmental hazard due to the excessive amounts of dust created, and thus, protective equipment must often be provided to insure the safety of personnel in the area of the surface treating operation.
As an alternative, it has been proposed to employ centrifugal blasting wheels to propel particulate abrasive material at high velocity against the surface being treated and to recover the abrasive for reuse. Apparatus employing centrifugal blasting wheels and means for recovery of spent abrasive material are disclosed, for instance, in U.S. Pat. No. 3,691,689. In accordance with that patent, spent abrasive material is swept into a collection bin by a rotating broom positioned behind the blast area. Such apparatus have significantly decreased the operating costs for treating surfaces, and since the blast area can be enclosed, the escape of dust from the system can be minimized, thereby increasing the safety of personnel in the area of treatment as compared to conventional air blasting operations.
Other proposals for surface treating apparatus have included the use of the kinetic energy of the abrasive material to rebound abrasive material from the surface being treated to a collection hopper for gravity feed to a centrifugal throwing wheel. For instance, in U.S. Pat. No. 3,977,128 to James R. Goff, there is disclosed an abrasive material throwing machine wherein abrasive material is projected by a centrifugal throwing wheel to impact the surface being treated at an inclined angle and has a predetermined angle of rebound into a rebound path. In order to direct the rebounding abrasive material to a storage hopper which is positioned above the centrifugal throwing wheel, rotary brushes are employed.
Some problems which have characterized blasting apparatus, such as those discussed above, employing abrasive materials for cleaning purposes result from the rather large size and complexity of the apparatus. This has created difficulty in cleaning areas confined by wall space or otherwise constricted, made these apparatus more difficult to move from one location to another, created problems of storage between operations and rendered the apparatus unusually costly.
Many of these apparatus have employed a blast pattern and recovery path which forces the abrasive material substantially out of the plane of rotation of the centrifugal wheel, propelling the abrasive material through a convoluted path, before it is returned to a hopper for redelivery and reuse. This involves a change of direction from the natural flow path the abrasive material would otherwise take.
Portions of the apparatus employed to effect such a change in direction are subjected to unusual wear and elevators or other recovery apparatus are required to insure that the abrasive material is returned to the hopper for redelivery. To accommodate this wear through the use of liners and heavier gauge metals and to provide the additional apparatus for recovery and redelivery raises the cost of the operation as well as the power requirements for the centrifugual wheel.
Many of the prior art blasting apparatus employ a centrally fed centrifugal wheel driven by a motor for propelling the abrasive toward the surface to be treated. The use of this type of apparatus has certain limitations imposed by the centrifugal wheels which limitations ultimately adversely affect the cleaning capcity of the abrasive. With a centrifugal wheel the speed with which the wheel can be driven is somewhat limited. The blades tend to break off at relatively high speeds, jam the system, and otherwise adversely effect the propulsion or kinetic energy imparted to the abrasive. By limiting the speed of the centrifugual wheel to avoid the breaking of the blades and other adverse effects, there is a corresponding limitation in the force or kinetic energy that can be imparted to the abrasive material. This, of course, derogates from the overall effectiveness of the blasting apparatus. Moreover, apparatus of this type normally employs an impeller and a control cage both of which can be eliminated with the apparatus of this invention.
By the apparatus of this invention the problems and limitations of the prior art apparatus discussed above have been overcome and a much more efficient, effective and compact cleaning apparatus, with reduced wear, has been provided.